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Mad Bull screaming gearbox

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Out with the Mad Bull yesterday and two packs into the run, the gearbox started squealing. Stripped it down this morning and just gave it another run. Started screaming after one pack. Diff is smooth, no collapsed bearings, gears all tip top, motor meshed properly. Stumped. Any suggestions as to what the source might be? 

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What type of motor are you running?  It's always possible the bushings (silver can, sport tuned brushed motors) or ball bearings (rebuilding brushed motor, brushless motor) need some lubrication.  Motors will make some terrible noises if they aren't lubricated.

Are you using a steel pinion or the aluminum pinion that came with the kit?  Aluminum pinions will wear and make a gearbox louder too; a steel pinion is much better.

Are you running ball bearings or the nylon bushings that came with the kit?  Nylon bushings have too much friction and can wear down; ball bearings are essential.

Another thought -- are you having any issues with the wheel nuts loosening?  If they loosen, the splined shafts will slip inside the wheel hexes and eventually kill the mating splines.  New nylock nuts or serrated wheel nuts will help.

The gears themselves should be fine.  The mesh is set by the gearbox halves, and the diff unit is pretty robust.  It's the motor, pinion, bearings, and wheel hexes that need the most consideration.

 

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Have you tried running the motor whilst not attached to the gearbox?

Thinking maybe it's the motor making a noise and not the gearbox. Possibly a stone or bit of grit has got into it.

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Gearbox is all bearings, as are the axles. Motor is stock silver can in this MB. I will try and see if it screams when not hooked up to the gearbox. The pinion is steel and properly meshed. 

I will check all the nuts, hadn't thought of that. 

Thanks for the replies guys, food for thought.

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Thought I would update this for future reference. 

It turns out that it was the motor screaming. It only started after running for a few minutes and seemed worse when the motor was not under stress, i.e. When slowing without braking. 

Hope this is helpful for someone in the future. 

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Light oil, like sewing machine oil, put a couple of drops on the bronze bushings on the motor with it on its side and have it running.

I use Hob-E-Lube which comes in various viscosities, usually used by the train guys.

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